textproduct: Rapid City

KEY MESSAGES

- Showers will gradually decrease in coverage overnight.

- Areas of fog will continue through Monday morning. Reduced visibilty expected around the Black Hills and across the western South Dakota plains for the Monday morning commute.

- More clouds than sun to start the week, followed by warmer and drier conditions later in the week.

DISCUSSION

(This Afternoon Through Saturday) Issued at 1144 AM MDT Sun Sep 20 2026

Water vapor and upper level analysis depicts a low centered over Wyoming, a ridge extending up the West Coast, and another low just off-shore of California. At the surface, the low is over the western Nebraska Panhandle with a weak trough extending northwestward along the Bighorns. Latest radar imagery has a large swath of rain over the western and central South Dakota plains, rotating counter- clockwise around the upper low.

For the rest of today, the main band of rain over the South Dakota plains will continue to lift northward, being replaced by a few smaller, less organized showers for the afternoon and evening hours. Rain showers across northeastern Wyoming will be less, as drier gets pulled up from southeastern Wyoming. High temperatures will remain cool with the damp conditions and abundant cloud cover, with no deviation from blended guidance which is close to current temps.

The upper low opens up and drifts east overnight, which will in-turn ends the rain showers from west to east. Lingering moisture in the air, combined with surface pressure rises and light winds, will result in areas of fog and low clouds into Monday morning. Visibility will gradually improve late Monday morning, with the lower ceilings and clouds sticking around throughout the day.

More clouds and some fog for MOnday night/Tuesday across the South Dakota Plains and the southern Black Hills - with the Northern Black Hills and portions of northeastern Wyoming becoming sunny. Clouds will gradually decrease across the entire area through the day, with increasing south-southeasterly winds. The strongest winds, 15 to 25 mph, will likely be across northwestern South Dakota where the pressure gradient looks to be the tightest.

A weak shortwave trough moves through Wednesday and Wednesday night, which could result in some showers across the area. The wave moves through fairly quickly, thus, some areas should remain dry.

A drier, warmer pattern then sets up for the end of the week into the weekend, with highs about 5 to 10 degrees above average.

AVIATION

(For the 18Z TAFS Through 18Z Monday) Issued At 1126 AM MDT Sun Sep 20 2026

An upper level low continues to spin over the SD/WY border, supporting widespread BR/DZ and showers today. Start time is not certain yet, currently targeting early afternoon, and will last into the evening. Ceilings will remain IFR through the forecast period. Some transient bands of slightly higher/lower visibility will be possible tied to any stronger areas of showers.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.